Demands on the information transmission bandwidths are always in an explosive growth rate. To accommodate the rapid development of network traffics, in backbone networks, 40 Gbps and 100 Gbps optical networks start deployments for commercial use, and 400 Gbps or 1 Tbps optical communication systems are under research and development. With respect to the access network, higher requirements would be definitely imposed on network traffic and multi-service support. At present, the access network is mainly based on the tree-structured passive optical network (PON), and the time division multiplexing-passive optical network (TDM-PON) is extensively applied. The Ethernet passive optical network (EPON) and the Gigabit-capable passive optical network (GPON) are mainstream means for network instruction of current Fiver To The Home (FTTH). However, neither the EPON nor the GPON accommodates the requirements on information rate imposed by the access network. Therefore, a next-generation PON technology has been widely concerned in the industry.
It is considered in the industry that the NG-PON may evolve towards three aspects: 1) single wavelength rate increase; 2) wave division multiplexing; and 3) orthogonal frequency division multiplexing. Technologies in the above three aspects may all effectively solve the bottleneck of bandwidth in the future market. However, in these technologies, some difficulties also need to be solved. For example, increasing the single wavelength rate may inevitably cause greater line dispersion. The orthogonal frequency division multiplexing imposes new requirements on digital signal process (DSP). Comparatively, the wave division multiplexing may be more easily implemented, the technical barrier is small and the cost is low. Accordingly, the Full Service Access network (FSAN) Summit finally determines the time- and wavelength-division multiplexed passive optical network (TWDM-PON) as a final solution of the next-generation PON products.
However, even the TWDM-PON likewise has some technical problems to be urgently solved. That is, wavelength division and time division functions are also implemented at the transmitter end of an ONU module, which is fresh in the access network. In the case of burst turn-on of a light source, since the chip has a high temperature and a variable refractive index, redshift of the operating wavelength occurs at the instant of burst turn-on. Since the dense wavelength division multiplexing (DWDM) system has a wavelength interval of generally 2000 G, 100 G or 50 G. Such redshift of the wavelength causes the optical signal to be transmitted into adjacent DWDM channels to form crosstalk, thereby lowering the communication quality.
With respect to this problem, literatures such as “High extinction switching of SOAs for in-band crosstalk reduction in PON” in Electronics letters published on Jul. 3, 2008 has proposed a service-oriented architecture (SOA) is integrated before a transmit DWDM laser, and the SOA is used as a burst unit. In this way, in the case of burst, the laser does not need to be turned on or turned off. This prevents impacts caused to the operating state or the operating wavelength of the laser in the case of burst.